Process for the non-destructive inspection of surface defects

ABSTRACT

In a process for the non-destructive inspection of surface defects, initially a solution with one or more dyes substantially having no emission under UV-light are applied and excess solution is removed after the dye has penetrated the surface defects, the surface is then covered with a developer leaving behind an absorbent coating with a high-contrast in daylight and which exclusively has one or more optical brighteners in a proportion between 0.02 and 2.0% by weight. The coating absorbs the dye from the surface defects, which appear as black traces on the coating under UV-light.

BACKGROUND OF THE INVENTION

The present invention relates to a process for the non-destructiveinspection of surface defects, in that initially a solution with one ormore dyes essentially having no emission under UV-light is applied andexcess solution is removed after the dye has penetrated the surfacedefects and then the surface is covered with a developer leaving behindan absorbent coating and which contains at least one fluorescentcomponent, the surface defects being revealed under UV-light asblackened portions within the light-emitting ambient.

For the non-destructive inspection or detection of surface defects,particularly on metal surfaces, the so-called red/white process isfrequently used and consists of applying a solution with a dye having ahigh contrast in daylight to the surface, so that solution and dye canpenetrate the surface defects. The excess solution is then removed fromthe surface, so that no dye residues are left behind. A coating is thenapplied, which leaves behind a background contrasting with the dye. Forexample, it can be a solvent with dispersed talc. After drying thecoating, and surface defects are revealed by the coloring of theabsorbent talc with the dye left behind in the surface defects.

A supplement to this process has been proposed for showing very smallsurface defects, such as cracks and the like (U.S. Pat. No. 3,564,249).In this process, following the wiping off of the dye applied, adeveloper is applied, which once again leaves behind a contrasting, e.g.approximately white and absorbent coating. This developer additionallycontains a fluorescent component, which emits under UV-light. Theabsorbent component of the coating, which can also consist of talc, onceagain removes the dye from the surface defects. A complementary color isformed at the corresponding points from the dye and the fluorescentcomponent and appears as a blackened portion under UV-light. Theseblackened portions can be detected clearly and in a sharply definedmanner even when the red/white process leaves behind no or only unclearcolorings. It is also pointed out that it need not be exclusively a reddye and also dyes in the blue range can be considered.

The known developer should contain approximately 1.5% of the essentialcomponent Fluoral 7 GA (product of General Aniline and FilmCorporation). It is also proposed to add 3.2% of an optical brightener,in addition to the fluorescent dye.

Fluoral 7 GA and similar fluorescent dyes give the coating a strikingyellow coloring, which impairs contrast in daylight. The problem to besolved by the present invention is to permit a better contrast withinthe coating.

SUMMARY OF THE INVENTION

On the basis of the aforementioned process, this problem is solved inthat the fluorescent component is solely constituted by one or moreoptical brighteners in a proportion between 0.02 and 2.0% by weight ofthe total weight of the developer.

Practical tests with the developer having a composition according to theinvention and which contains as the fluorescent component solely anoptical brightener which is invisible in daylight in a much largerproportion compared with the Prior Art, have shown that the coatingprovides a high-contrast background both for the red/white process andfor the UV-process, so that surface defects in daylight are made readilyapparent by the red coloring and in UV-light by the blackening. Inaddition, fluorescent dyes are relatively expensive, whereas opticalbrighteners are used on an industrial scale in washing and bleachingagents and are consequently inexpensive. Thus, the invention not onlyprovides an agent with improved use characteristics and consequently amore precise inspection process, but in addition the developer can alsobe produced less expensively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a preferred embodiment, the optical brightener is added tothe developer in a proportion of 0.05 to 0.5% by weight. This makes itclear how small the added optical brightener quantity can be withouthaving to accept losses in the precision of the inspection process.

The developer may comprise 70 to 95% by weight solvent, 5 to 30% byweight talc, 0 to 1.0% by weight wetting agent and 0.05 to 0.5% byweight optical brightener.

According to an embodiment, the developer consists of 88.8% by weightsolvent, 11.0% by weight talc, 0.1% by weight wetting agent and 0.1% byweight optical brightener.

All industrially available optical brighteners can be used for theprocess according to the invention. These optical brighteners absorblong-wave UV-light in the range 350 to 390 nm and emit light in thevisible range between 420 and 500 nm. A specific example is 7-Diethylamino-4-methyl-kumarin.

The process according to the invention can not only be used for theinitial inspection of surfaces, but also as a checking process for theaforementioned red/white or UV-processes. In this process, initially asolution with one or more dyes having substantially no light emissionunder UV-light are applied, excess solution is removed after the dye haspenetrated into the surface defects and then an absorbent coating havinga contrast under daylight is applied. It is then possible to detect theareas of the coating which have become colored by the dye under daylightor UV-light. Sources of error not infrequently occur in such processesbecause colorings with only a limited contrast are obtained and are thendifficult to interpret. There can also be discontinuities in thecoloring, in that e.g. microflaws on the coating do not appear as acontinuous line and instead give individual punctiform coloring zones,so that in conjunction with other surface defects also leading topunctiform or zonal colorings, it is not possible to conclude that thereis a crack.

According to a preferred embodiment when there are uncertainties or lackof clarity regarding the representation of surface defects by one of theknown processes, it is proposed that the area surrounding the coloredzones providing dubious information are removed from the coating,preferably by wiping off and is followed by the application of thedeveloper according to the invention, which contains as the solefluorescent component at least one optical brightener in a proportionbetween 0.02 and 2.0% by weight of the total developer weight.

This process makes it possible to check in a planned manner areasproviding doubtful information and resulting from the red/white orUV-process. It has been found that after wiping off the coating from thefirst process, there is still an adequate dye reserve in the surfacedefects to ensure an adequate penetration of the optical brightener intothe coating, so that then there is a completely satisfactory blackeningaction under UV-light, which provides reliable information on the natureof the surface defect.

Isopropanol can be used as a solvent for the developer according to theinvention. It is also possible to use 1,1,1-Trichloroethane and mixturesof solvents. A wetting agent which has proved satisfactory isEthoduomeen T 13 (Akzo product and trademark) and this is based on talloil. Not only talc can be used as the absorbent, contrast-givingcomponent of the coating and it is also possible to use other inertpowders, such as amorphous silicon dioxide or magnesium carbonate, whichhave given good results.

I claim:
 1. A process for the non-destructive inspection of surfacedefects, where initially a solution with one or more dyes havingsubstantially no emission under UV-light is applied to the surface beinginspected and the excess solution is removed after the dye haspenetrated the surface defects of the surface being inspected, thesurface is then coated with an absorben fluorescent developer leavingbehind an absorbent fluorescent developer coating that in daylight is inhigh contrast to the color to the color of the dye initially applied andcontains at least one fluorescent component such that the absorbentfluorescent developer coating fluoresces under UV-light, so that whenUV-light is applied to said surface being inspected its surface defectsappear thereunder as blackened portions within the lightemitting ambientresulting from fluorescing by the absorbent fluorescent developercoating, the improvement being that the absorbent fluorescent developerused has its at least one fluuoescent component exclusively constitutedby at least one optical brightener in a proportion between 0.02 and 2.0%by weight of the total absorbent fluorescent developer weight. 2.Process according to claim 1, characterized in that, optical brighteneris added in a proportion of 0.05 to 0.5% by weight to the totalabsorbent flourescent developer weight.
 3. Process according to claims 1or 2, characterized in that, the absorbent flourescent developercomprises 70 to 95% by weight solvent, 5 to 30% by weight talc, 0 to1.0% by weight wetting agent and 0.05 to 0.5% by weight opticalbrightener.
 4. Process according to claim 3 wherein between the steps ofremoving the excess solution and applying the absorbent fluorescentdeveloper, an absorbent coating having a color that in daylight is inhigh contrast to the color of the dye initially applied is applied, dyecolored areas of the coating are examined and any areas of doubtfulinformative character surrounding the colored areas are removed. 5.Process according to claim 4, wherein the dye colored areas of thecoating are examined under daylight.
 6. Process according to claim 4,wherein the dye colored areas of the coating are examined underUV-light.
 7. Process according to claim 4, wherein the areas of doubtfulinformative character surrounding the colored areas are removed bywiping.
 8. Process according to claim 4, wherein after the absorbentfluorescent developer is applied, the surface is inspected underUV-light.
 9. Process according to claim 3, wherein the solvent is atleast one material selected from the group consisting of isopropanol and1,1,1-Trichloroethane.
 10. Process according to claim 3, wherein thewetting agent is based on tall oil.
 11. Process according to claims 1 or2 wherein between the steps of removing the excess solution and applyingthe absorbent fluorescent developer, an absorbent coating having a colorthat in daylight is in high contrast to the color of the dye initiallyapplied is applied, dye colored areas of the coating are examined andany areas of doubtful informative character surrounding the coloredareas are removed.
 12. Process according to claim 11, wherein the dyecolored areas of the coating are examined under daylight.
 13. Processaccording to claim 11, wherein the dye colored areas of the coating areexamined under UV-light.
 14. Process according to claim 11, wherein theareas of doubtful informative character surrounding the colored areasare removed by wiping.
 15. Process according to claim 11, wherein afterthe absorbent fluorescent developer is applied, the surface is inspectedunder UV-light.
 16. Process according to claim 1, wherein the at leastone optical brightener is 7-Diethylamino-4-Methyl-Kumarin.
 17. Processaccording to claim 1, wherein the absorbent fluorescent developercontains an absorbent selected from the group consisting of talc,silicon dioxide and magnesium carbonate.